Each of the applications, patents, and papers cited in this application and in co-pending U.S. application Ser. No. 10/961,814, U.S. application Ser. No. 11/952,848, U.S. application Ser. No. 11/952,856 as well as each document or reference cited in each of the applications, including during the prosecution of each co-pending patent application and each of the PCT and foreign applications or patents corresponding to and/or claiming priority from any of these applications and patents, and each of the documents cited or referenced in each of the application cited documents, are hereby expressly incorporated herein.
For scale up of adherent cell culture, multiple shelf flasks such as the Nunc Cell Factory and Corning® Cell Stack are commonly used. However, to provide oxygen to the cells during culture, these devices require each shelf to have gas reside above the medium. This need for gas to be present in the device makes the device large and awkward to handle during scale up, wasting laboratory space and requiring the use of special equipment during media exchange. The net result is a complicated and costly process as cultures increase in size. The need for a gas-liquid interface to oxygenate the culture is the root cause of these inefficiencies.
Co-pending U.S. patent application Ser. No. 10/961,814 (Wilson et al.) describes multiple shelf devices that eliminates the need for gas to reside above each shelf. In one embodiment, a series of shelf-like scaffolds for cells to reside upon are arranged one above the other and at least a portion of the outer wall(s) of the device is gas permeable. The gas permeable outer wall(s) is oriented perpendicular to the scaffolds. Gas transmission through the gas permeable outer walls(s) allows cells to be oxygenated in the absence of a gas-liquid interface. The culture can proceed without need to perfuse media or gas (i.e. operates in a static mode), allowing a simple cell production method. However, as the device gets wider, the distance a cell can get from the oxygen source increases. At some point, a cell can get too far from the oxygen source and the device scalability in the horizontal direction becomes limited. Thus, although the device is more compact than traditional devices, its scalability in the horizontal direction is limited.
Co-pending U.S. patent application Ser. No. 11/952,848 (Wilson) also describes devices that eliminate the need for gas to reside above each shelf. In various embodiments, a series of cell compartments are arranged one above the other. The bottom of each cell compartment is gas permeable. In use, cells can reside upon the gas permeable surfaces, which act to function as gas permeable scaffolds. This allows each cell to be a uniform distance from the ambient oxygen source as the devices scales horizontally and vertically. However, this type of device can be more difficult and expensive to manufacture than the devices described in co-pending '814, elevating its cost to the end user. Furthermore, since more gas permeable surface area is present, evaporation of media in the device can occur at a higher rate than the traditional multiple shelf flask and the devices of co-pending '814. Configurations are disclosed that minimize this problem, but they add features that increase cost.
Although co-pending '848 and co-pending '814 provide a more space efficient geometry than traditional multiple shelf flasks, there are cell culture applications for which neither co-pending '848 nor co-pending '814 are ideal. As just one example, stem cells are often cultured at low surface density so that cells do not get too close to each other in order to prevent unwanted differentiation. As the number of cells that the culture is intended to generate increases, the culture device needs to provide a larger amount of surface area to keep the cells at low surface density. Therefore, a device that allows scale up in the vertical and horizontal direction is useful. To make the most efficient use of space, it should function in the absence a gas-liquid interface and not require equipment to pump media or gas through it. Although co-pending '848 provides those attributes, the extra cost to place cells a uniform distance from ambient gas is not warranted since few cells are present for each square centimeter of area that cells reside upon (i.e. low oxygen demand). The lower cost devices of co-pending '814 have limited scalability in the horizontal direction. Thus, a new device configuration is needed that is inexpensive to manufacture, easy to use, eliminates the need for a gas-liquid interface, does not require perfusion, and fills the void between co-pending '848 and co-pending '814. Such a device would cost reduce and simplify the cell manufacturing process for many important cell culture applications such as stem cell culture.
Accordingly, an improved gas permeable device is disclosed that is easy to manufacture, can function in the absence of a gas-liquid interface, does not require equipment to pump media or gas through it, and allows virtually unlimited scalability in the horizontal and vertical direction.